The World's 18 Strangest Tunnels: Gallery

Life aboveground is crowded. As engineers and architects grapple with innovative ways to meet the needs of roads, superhighways and bridges to handle unprecedented traffic. But sometimes, going underground is the only option. Tunnels, whether bored through imposing mountains or laid hundreds of feet under water, are inspiring feats of engineering. Here, PM presents a collection of the world's most interesting and impressive tunnels.

1: Laerdal Tunnel

1: Laerdal Tunnel

Location /// Sogn og Fjordane, Norway

Background: About 5000 different blasts were conducted during the construction phase of Laerdal Tunnel, which stretches under Norway's mountainous and fjord-filled terrain for 15 miles, making it the longest completed road tunnel in the world.

Why It's Unique: Driving through a windowless tunnel for 20 minutes can get a bit monotonous, so a team of psychologists and engineers focused on retaining driver concentration. "The psychological reaction of a person in a tunnel is very important ... it makes the difference between people accepting the facility or simply just avoiding it," says Youssef Hashash, a professor of Civil and Environmental Engineering at the University of Illinois, who has worked on 10 different tunnel projects. "Given the length of this tunnel, you need a carefully designed environment and lighting system." Some solutions used in the Laerdal tunnel include bright blue lights and subtle curves that keep drivers engaged. Most important, though, is the fact that the tunnel is divided into several different sections, breaking up the drive and creating the impression that commuters are traveling through a handful of smaller tunnels.

2. Channel Tunnel

2. Channel Tunnel

Background: Commonly known as the Chunnel, this behemoth structure links England and France. Completed in 1994, the price tag of this 31-mile-long tunnel exceeded $20 billion.

Why It's Unique: Linking France and England via the English Channel is an idea that has been kicking around for hundreds of years. "There were previous attempts to build a tunnel here, but they were stopped for a variety of reasons, both technical and political," Hashash says. The advent of modern boring machines and the indisputable economic benefit of joining the two countries helped bring the concept to fruition, resulting in one of the most impressive demonstrations of engineering prowess of all time. To account for hazards such as fires--and there have been several within the tunnel since it was built--the designers built a smaller service tunnel in between the two main tubes to act as an escape route.